Roc Meseguer

Topology patterns of a community network: Guifi.net

This paper presents a measurement study of the topology and its effect on usage of Guifi.net, a large-scale community network. It focuses on the main issues faced by community network and lessons to consider for its future growth in order to preserve its scalability, stability and openness. The results show the network topology as an a typical high density Scale-Free network with critical points of failure and poor gateway selection or placement. In addition we have found paths with a large number of hops i.e. large diameter of the graph, and specifically long paths between leaf nodes and web proxies. The usage analysis using a widespread web proxy service confirms that these topological properties have an impact on the user experience.

Modeling IoT-Based Solutions Using Human-Centric Wireless Sensor Networks

The Internet of Things (IoT) has inspired solutions that are already available for addressing problems in various application scenarios, such as healthcare, security, emergency support and tourism. However, there is no clear approach to modeling these systems and envisioning their capabilities at the design time. Therefore, the process of designing these systems is ad hoc and its real impact is evaluated once the solution is already implemented, which is risky and expensive. This paper proposes a modeling approach that uses human-centric wireless sensor networks to specify and evaluate models of IoT-based systems at the time of design, avoiding the need to spend time and effort on early implementations of immature designs. It allows designers to focus on the system design, leaving the implementation decisions for a next phase. The article illustrates the usefulness of this proposal through a running example, showing the design of an IoT-based solution to support the first responses during medium-sized or large urban incidents. The case study used in the proposal evaluation is based on a real train crash. The proposed modeling approach can be used to design IoT-based systems for other application scenarios, e.g., to support security operatives or monitor chronic patients in their homes.

Cloud-Based Extension for Community-Lab

Community-Lab is an open, distributed infrastructure for researchers to carry out experiments within wireless community networks. Community networks are an emergent model of infrastructures built with off-the-shelf communication equipment that aims to satisfy a communitys demand for Internet access and ICT services. Community-Lab consists of more than 100 nodes that are integrated in existing community networks, thus giving researchers access to community networks and allowing them to conduct experimental evaluation of routing protocols, services and applications deployed there. Community networks have now the opportunity to extend the collaborative network building to the next level, that is, building collaborative services implemented as community clouds, built, operated and maintained by the community, that run on community-owned heterogeneous resources, and offer cloud-based services that are of the communitys interest. This demo paper focuses on demonstrating the cloud extension of Community-Lab, enabling now community cloud experiments. By means of selected applications, we show how Community-Lab has been extended with distributed clouds, where different devices such as server, desktop PCs, low-resource embedded PCs and IoT boards are brought together forming a heterogeneous distributed cloud environment for researchers to experiment in community networks.

Reducing energy consumption in human-centric wireless sensor networks

Energy consumption is a main research issue in wireless sensor networks; and particularly in those where nodes collaborate to reach a goal. This article explores the energy consumption in mobile devices participating in a human-based wireless sensor network. Specifically, the paper proposes the use of a message predictor to help detect and reduce the number of unnecessary control packets delivered by the nodes as a way to keep updated the network topology. In order to evaluate this proposal, the Optimized Link State Routing protocol was modified to add a message predictor between the routing and the network layers. Eleven simulations were performed using a particular setting. The preliminary results indicate the use of the message predictor can help reduce considerably the nodes energy consumption without affecting the routing capability of the protocol. Although these results are still preliminary, they are highly encouraging.

Exploring local service allocation in community networks

Community Cloud computing is a new trend on cloud computing that aims to build service infrastructures upon Wireless Community Networks taking advantage of underused community physical resources. Service allocation protocols are a key design challenge that all cloud systems must properly address to optimize resource utilization. They are specially important when cloud services require a Quality of Service (QoS) and network stability or performance (delay, jitter, minimum bandwidth) cannot be guaranteed a-priory. This work presents a study that tries to understand how to address cloud service deployments in such scenario. In particular, we start proposing an allocation algorithm to find optimal solutions when there is a central authority that coordinates the process. These solutions optimize the communication cost in two ways: (1) minimizing the service overlay diameter and, (2) minimizing the coordination cost along the network. Based on the study of the algorithm and the experimental simulations, we study the variables that outcome optimal service allocations to the detriment of other solutions. We verify these findings using data mining techniques. Researchers can take advantage of the simulation results and our observations to design more reliable distributed algorithms able to dynamically self-adapt to network changes.

Effort-based incentives for resource sharing in collaborative volunteer applications

Collaborative and volunteer applications need to implement incentive mechanisms to regulate resource sharing and encourage network nodes to contribute for reaching a certain goal. Typically, these incentive mechanisms assign resources to network node requests, based on the total amount of resources contributed by the requesting participant. This approach assumes that participants contributing more should also get back more resources from the collaborative environment. This assumption turns the system unfair to those participants with scarce resources, because they have just few resources to share. This paper proposes the use of an incentive strategy based on the contribution percentage of each node; i.e. an effort-based approach. This proposal is evaluated and compared to contribution-based strategies. The obtained results show that the proposed effort-based approach not only benefits participants that have scarce resources, but also it is able to satisfy the requests of the powerful nodes.

OLSRp: Predicting Control Information to Achieve Scalability in OLSR Ad Hoc Networks

Scalability is a key design challenge that routing protocols for ad hoc networks must properly address to maintain the network performance when the number of nodes increases. We focus on this issue by reducing the amount of control information messages that a link state proactive routing algorithm introduces to the network. Our proposal is based on the observation that a high percentage of those messages is always the same. Therefore, we introduce a new mechanism that can predict the control messages that nodes need for building an accurate map of the network topology so they can avoid resending the same messages. This prediction mechanism, applied to OLSR protocol, could be used to reduce the number of messages transmitted through the network and to save computational processing and energy consumption. Our proposal is independent of the OLSR configuration parameters and it can dynamically self-adapt to network changes.

Analysis of the Social Effort in Multiplex Participatory Networks

Community networks are participatory connectivity solutions for citizens where all the resources are owned, managed and controlled by the participants. As a natural evolution, in recent years some initiatives have flourished to provide higher level services based on volunteer computing and resource sharing paradigms. A fundamental aspect of these paradigms is user participation. In this work, we apply some social mining techniques aiming to identify the roles of the individuals in the social network behind a community network, here Guifi.net, and to measure the participatory involvement in the community network from 2003 to 2014. We observed that community network participants generally dedicate their time and effort to a single participatory forum, generating several types of community structures. We analyzed such structures using a multiplex network formed by mailing list in Guifi.net and a relationship graph built pairwise of users that share a physical wireless link. We were able to distinguish between non-hierarchical participatory forums, where almost all users are part of the same big community and two-tier participatory forums leaded by a small number of users that act as social bridges between their members. Finally, by testing the impact of community leaders in all participatory layers, we profiled the utility of the members’ effort to the whole wireless community network.

Internet Access for All: Assessing a Crowdsourced Web Proxy Service in a Community Network

Global access to the Internet for all requires a dramatic reduction in Internet access costs particularly in developing areas. This access is often achieved through several proxy gateways shared across local or regional access networks. These proxies allow individuals or organisations to share the capacity of their Internet connection with other users. We present a measurement study of a crowdsourced Internet proxy service in the guifi.net community network that provides free Web access to a large community with many small proxy servers spread over the network. The dataset consists of Squid proxy logs for one month, combined with network topology and traffic data. Our study focuses on a representative subset of the whole network with about 900 nodes and roughly 470 users of the web proxy service. We analyse the service from three viewpoints: Web content traffic from users, performance of proxies and influence of the access network. We find clear daily patters of usage, excess capacity and little reuse of content which makes caching almost unnecessary. We also find variations and small inefficiencies in the distribution of traffic load across proxies and the access network, related to the locality and manual proxy choice. Finally, users experience an overall usable Internet access with good throughput for a free crowdsourced service.

Real-Time Communication Support for Underwater Acoustic Sensor Networks

Underwater sensor networks represent an important and promising field of research due to the large diversity of underwater ubiquitous applications that can be supported by these networks, e.g., systems that deliver tsunami and oil spill warnings, or monitor submarine ecosystems. Most of these monitoring and warning systems require real-time communication in wide area networks that have a low density of nodes. The underwater communication medium involved in these networks is very harsh and imposes strong restrictions to the communication process. In this scenario, the real-time transmission of information is done mainly using acoustic signals, since the network nodes are not physically close. The features of the communication scenario and the requirements of the communication process represent major challenges for designers of both, communication protocols and monitoring and warning systems. The lack of models to represent these networks is the main stumbling block for the proliferation of underwater ubiquitous systems. This paper presents a real-time communication model for underwater acoustic sensor networks (UW-ASN) that are designed to cover wide areas with a low density of nodes, using any-to-any communication. This model is analytic, considers two solution approaches for scheduling the real-time messages, and provides a time-constraint analysis for the network performance. Using this model, the designers of protocols and underwater ubiquitous systems can quickly prototype and evaluate their solutions in an evolving way, in order to determine the best solution to the problem being addressed. The suitability of the proposal is illustrated with a case study that shows the performance of a UW-ASN under several initial conditions. This is the first analytic model for representing real-time communication in this type of network, and therefore, it opens the door for the development of underwater ubiquitous systems for several application scenarios.